Download galaxies and stars - Valhalla High School

• The Universe
Big Bang Theory
• According to the Big
Bang Theory, the
universe formed in an
enormous explosion
about 10 to 15 billion
years ago.
• The universe has
been expanding ever
since.
Galaxies
• The Milky Way is the galaxy in which our
solar system is located.
• A galaxy is a giant structure that contains
billions of stars.
• The farther away a galaxy is from us, the
faster it is moving.
• It takes 2 million years for light from the
Andromeda galaxy to reach earth.
• Astronomers have classified most galaxies
into three main categories: spiral, elliptical
and irregular.
Spiral Galaxies
Elliptical Galaxies: only old stars
Irregular Galaxies
Nebula
• About five billion
years ago a giant
cloud of gas and dust,
or nebula, collapsed
to form the solar
system.
• Slowly the nebula
shrank to form a
spinning disk.
Star Systems
• More than half of all stars are members of
groups of two or more stars
• Binary systems have two stars
• A system where one star blocks the other
is an eclipsing binary
• A system with three stars is a triple star
system
Stars
• The Milky Way contains hundreds of
billions of stars
• Distances to stars are measured in light
years.
• A light year is the distance light travels in
one year—9.5 million million kilometers
Classifying Stars
¤ All stars are huge spheres of glowing gas
¤ They are made up mostly of hydrogen
¤ They all engage in nuclear fusion
¤ The sun appears brightest because it is
closest to Earth
¤ The main characteristics used to classify
stars are size, temperature and
brightness.
Sizes of stars
• The sun is a medium size star
• Some stars are very large—giants and
supergiants
• Some stars are smaller than the sun—
white dwarf stars, neutron stars
• White dwarf stars are the size of Earth and
neutron stars are smaller
Color and Temperature of Stars
• A star’s color reveals its temperature
• The coolest stars appear reddish, about
3,200 degrees Celsius
• The hottest stars appear bluer than the
sun, over 10,000 degrees Celsius
• The sun has a surface temperature of
about 5,000 degrees Celsius
Brightness of Stars
• Stars give off different amounts of light.
• How bright a star looks from Earth
depends on both how far it is and how
bright the star actually is.
• Brightness is described in two ways:
– Apparent magnitude
– Absolute magnitude
Magnitude
• A star’s apparent
magnitude is its
brightness as seen
from Earth
• A star looks brighter
the closer it is to
Earth
• A star’s absolute
magnitude is the
brightness a star
would have if it were
at a standard distance
from Earth.
Hertzsprung-Russell diagram
 The temperatures of stars are on the x axis and
the brightness is on the y axis.
 Most stars are on a diagonal line called the Main
Sequence, where surface temperature increases
as brightness increases.
 Giants and supergiants are higher and farther to
the right.
 White dwarfs are hot but not very bright so they
are at the bottom center.
Life and Death of Stars